Financial Instruments and Fair Value - Schedule of Fair Value of Financial Instruments Measured on Recurring Basis (Detail) - USD ($)
$ in Thousands
Apr. 30, 2019
Jan. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities $ 206,752 $ 205,106
Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 10,501 8,914
Certificates of Deposit [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 1,006 7,012
Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 67,998 68,233
Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 91,208 87,360
Asset-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 15,525 11,604
U.S. government securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 20,514 21,983
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 11,507 15,926
Level 1 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 10,501 8,914
Level 1 [Member] | Certificates of Deposit [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 1,006 7,012
Level 1 [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 1 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 1 [Member] | Asset-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 1 [Member] | U.S. government securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 195,245 189,180
Level 2 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 2 [Member] | Certificates of Deposit [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 2 [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 67,998 68,233
Level 2 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 91,208 87,360
Level 2 [Member] | Asset-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 15,525 11,604
Level 2 [Member] | U.S. government securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 20,514 21,983
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | Certificates of Deposit [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | Asset-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities 0 0
Level 3 [Member] | U.S. government securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable debt securities $ 0 $ 0